Certain mechanisms employ actuator arms or other mechanical members which are mounted for rotation on a shaft. It is frequently required that the member have a precise angular position with respect to the shaft. For example, in mechanisms which are used to open and close damper vanes within an air duct, the actuator arm must have a precise and maintainable angular position on the shaft so as to assure that the damper can reach its extreme open and closed positions.
Heretofore there have been a number of different mechanical connections employed between a shaft and its member, but in general, these provide incremental rather than continuous angular positions of the member with respect to the shaft. For example, the shaft may be splined with the member's bore splined to match. However, it can be easily seen that even a relatively large number of splines will still result in relatively large angles between sequential positions. Twenty splines on a shaft provide 18.degree. steps in angular position. The same situation results with a shaft having a regular polygonal cross section and a member having a conforming bore. Note that even an octagonal shaft cross section results in 45.degree. angles between adjacent member angular positions.
In the case of an arm member, it is also possible to provide an incrementally adjustable articulation for the arm, but this involves additional manufacturing costs. The use of set screws, pinch fittings, or other clamping mechanisms to attach the member to the shaft is usually not suitable if more than a nominal amount of torque is to be transferred.
Accordingly, there is a requirement for apparatus allowing an arm or other member to be securely fixed for rotation to a shaft at any one of an infinite number of angular positions.